40
configured, this capability will work to prevent over-cooling
the space during the occupied period.
Supply Air Set Point Control and the Staging of Compressors
— Once the control has determined that a cooling mode is in
effect, the cooling control point (
Run Status
→
VIEW
→
CL.C.P
) is calculated and is based upon the supply air set
point (
Setpoints
→
SASP
) plus any supply air reset being
applied (
Inputs
→
RSET
→
SA.S.R
).
Refer to the SumZ Cooling Algorithm section on page 43
for a discussion of how the A Series
Comfort
Link™ controls
manage the staging of compressors to maintain supply-air
temperature.
VAV Cool Mode Selection during the Unoccupied Period
(
C.TYP =
1,2;
Operating Modes
→
MODE
→
OCC=
OFF
)
and Space Sensor Cool Mode Selection
(
C.TYP=
5 and 6
) —
The machine control types that utilize this technique of mode
selection are:
•
C.TYP
= 1 (VAV-RAT) in the unoccupied period
•
C.TYP
= 2 (VAV-SPT) in the unoccupied period
•
C.TYP
= 5 (SPT-MULTI) in both the occupied and
unoccupied period
•
C.TYP
= 6 (SPT- 2 STG) in both the occupied and
unoccupied period
These particular control types operate differently than the
VAV types in the occupied mode in that there is both a LOW
COOL and a HIGH COOL mode. For both of these modes, the
control offers two independent set points,
Setpoints
→
SA.LO
(for LOW COOL mode) and
Setpoints
→
SA.HI
(for HIGH
COOL mode). The occupied and unoccupied cooling set points
can be found under
Setpoints
.
The heat/cool set point offsets are found under
Configura-
tion
→
D.LV.T
.
See Table 48.
Operating modes are under
Operating Modes
→
MODE
.
Cool Mode Evaluation Logic
— The first thing the control
determines is whether the unit is in the occupied mode (
OCC
)
or is in the temperature compensated start mode (
T.C.ST
). If
the unit is occupied or in temperature compensated start mode,
the occupied cooling set point (
OCSP
) is used. For all other
modes, the unoccupied cooling set point (
UCSP
) is used. For
further discussion and simplification this will be referred to as
the “cooling set point.” See Fig. 6.
Demand Level Low Cool On Offset
(
L.C.ON
) — This is the
cooling set point offset added to the cooling set point at which
point a Low Cool mode starts.
Demand Level High Cool On Offset
(
H.C.ON
) — This is the
cooling set point offset added to the “cooling set point plus
L.C.ON
” at which point a High Cool mode begins.
Demand Level Low Cool Off Offset
(
L.C.OF
) — This is the
cooling set point offset subtracted from “cooling set point plus
L.C.ON
” at which point a Low Cool mode ends.
NOTE: The “high cool end” trip point uses the “low cool off”
(
L.C.OF
) offset divided by 2.
To enter into a LOW COOL mode, the controlling tempera-
ture must rise above [the cooling set point plus
L.C.ON
.]
To enter into a HIGH COOL mode, the controlling temper-
ature must rise above [the cooling set point plus
L.C.ON
plus
H.C.ON
.]
To exit out of a LOW COOL mode, the controlling temper-
ature must fall below [the cooling set point plus
L.C.ON
minus
L.C.OF
.
]
To exit out of a HIGH COOL mode, the controlling temper-
ature must fall below [the cooling set point plus
L.C.ON
minus
L.C.OF
/2.]
Comfort Trending
— In addition to the set points and offsets
which determine the trip points for bringing on and bringing
off cool modes, there are 2 configurations which work to hold
off the transitioning from a low cool to a high cool mode if the
space is cooling down quickly enough. This technique is
referred to as Comfort Trending and the configurations of
interest are
C.T.LV
and
C.T.TM
.
Cool Trend Demand Level
(
C.T.LV
) — This is the change in
demand that must occur within the time period specified by
C.T.TM
in order to hold off a HIGH COOL mode regardless
of demand. This is not applicable to VAV control types
(
C.TYP
=1 and 2) in the occupied period. As long as a LOW
COOL mode is making progress in cooling the space, the con-
trol will hold off on the HIGH COOL mode. This is especially
true for the space sensor machine control types (
C.TYP
= 5
and 6), because they may transition into the occupied mode
and see an immediate large cooling demand when the set
points change.
Cool Trend Time
(
C.T.TM
) — This is the time period upon
which the cool trend demand level (
C.T.LV
) operates and may
hold off staging or a HIGH COOL mode. This is not applicable
to VAV control types (
C.TYP
=1 and 2) in the occupied period.
See the Cool Trend Demand Level section for more details.
Timeguards
—
In addition to the set points and offsets which
determine the trip points for bringing on and bringing off cool
modes there is a timeguard which enforces a time delay
between the transitioning from a low cool to a high cool mode.
This time delay is 8 minutes. There is a timeguard which
enforces a time delay between the transitioning from a heat
mode to a cool mode. This time delay is 5 minutes.
Supply Air Set Point Control
—
Once the control has deter-
mined that a cooling mode is in effect, the cooling control
point (
Run Status
→
VIEW
→
CL.C.P
) is calculated and is
based upon either
Setpoints
→
SA.HI
or
Setpoints
→
SA.LO
,
depending on whether a high or a low cooling mode is in
effect, respectively. In addition, if supply air reset is config-
ured, it will also be added to the cooling control point.
Refer to the SumZ Cooling Algorithm section for a discus-
sion of how the A Series
Comfort
Link™ controls manage
supply-air temperature and the staging of compressors for these
control types.
Table 48 — Cool/Heat Set Point Offsets Configuration
ITEM
EXPANSION
RANGE
UNITS
CCN
POINT
DEFAULT
OCSP
Occupied
Cool Setpoint
55-80
dF
OCSP
75
UCSP
Unoccupied
Cool Setpoint
75-95
dF
UCSP
90
ITEM
EXPANSION
RANGE
CCN POINT
MODE
MODES CONTROLLING UNIT
OCC
Currently Occupied
ON/OFF
MODEOCCP
T.C.ST
Temp.Compensated Start
ON/OFF
MODETCST
ITEM
EXPANSION
RANGE
UNITS
CCN POINT
DEFAULT
D.LV.T
COOL/HEAT SETPT. OFFSETS
L.H.ON
Dmd Level Lo Heat On
-1 - 2
^F
DMDLHON
1.5
H.H.ON
Dmd Level(+) Hi Heat On
0.5 - 20.0
^F
DMDHHON
0.5
L.H.OF
Dmd Level(-) Lo Heat Off
0.5 - 2
^F
DMDLHOFF
1
L.C.ON
Dmd Level Lo Cool On
-1 - 2
^F
DMDLCON
1.5
H.C.ON
Dmd Level(+) Hi Cool On
0.5 - 20.0
^F
DMDHCON
0.5
L.C.OF
Dmd Level(-) Lo Cool Off
0.5 - 2
^F
DMDLCOFF
1
C.T.LV
Cool Trend Demand Level
0.1 - 5
^F
CTRENDLV
0.1
H.T.LV
Heat Trend Demand Level
0.1 - 5
^F
HTRENDLV
0.1
C.T.TM
Cool Trend Time
30 - 600
sec
CTRENDTM
120
H.T.TM
Heat Trend Time
30 - 600
sec
HTRENDTM
120
Summary of Contents for WEATHERMAKER 48AJ020
Page 95: ...95 Fig 13 Typical Main Control Box Wiring Schematic A48 7787 ...
Page 96: ...96 TO NEXT PAGE Fig 14 Auxiliary Control Box Wiring Schematic A48 7294 ...
Page 98: ...98 Fig 15 Typical 2 Stage Gas Heat Wiring Schematic Size 051 and 060 Units Shown A48 6866 ...
Page 102: ...102 TO NEXT PAGE Fig 18 Typical Power Schematic Size 051 and 060 Units Shown A48 7298 ...
Page 104: ...104 Fig 19 Controls Option Wiring Schematic A48 7810 ...
Page 105: ...105 Fig 20 Small Chassis Component Location Size 020 035 Units A48 7301 ...
Page 106: ...106 Fig 21 Large Chassis Component Locations Size 036 060 Units A48 7302 ...